If Cayley is aviation's grandfather, Otto Lilienthal is its uncle. From
statements and writings left by the Wright brothers, it is clear Lilienthal
was an important source of inspiration for their efforts. A case can be made
that the writings of Lilienthal directly inspired the Wrights to take on the
invention of the airplane as an interesting pursuit. Certainly their early
framing of the "problem of flight" was derived largely from Lilienthal's ideas
and difficulties. Echoes from Lilienthal's article Practical Experiments
for the Development of Human Flight are clearly evident in Wilbur's
address to the Western Society of Engineers, and in his first letter to Octave
Chanute.

Before 1881, attempts to develop airplanes and gliders were occasional
and sporadic. Lilienthal changed all that. Indeed, Lilienthal's efforts broke
the 'respectability barrier' that haunted serious efforts to develop
airplanes. Before Lilienthal, building a heavier-than-air craft was widely
considered to be the province of dreamers and fools; afterwords it seemed
possible to fly. Thus, his efforts mark the beginning of the experimental
period of active research on heavier-than-air flight. Lilienthal developed
eighteen different models of his gliders over a span of 5 years. His
efforts received worldwide publicity, and his successes lent others the
courage to follow in his footsteps.

Fifteen of Lilienthal's gliders were monoplanes, three were biplanes.
Each model was a hang glider, controlled by the pilot shifting his weight
rather than through the use of any active control surfaces. These
eighteen craft will be described separately at
some point in the hopefully-not-too-distant future.

Sir Charles Gibbs-Smith divided airplane inventors into two categories.
The first he termed "Chauffeurs of the Air," because they acted as though
flying a plane was like driving a car. Maxim is the best example of this large
category. In contrast, Gibbs-Smith identified "Airmen" who understood that the
fluid medium of air made flight a quite different proposition than land-based
maneuvering. Chauffeurs tended to be concerned with obtaining sufficient
propulsion, without worrying overmuch about factors like lift or control.
Airmen often worked on gliders before tackling the problem of powered flight.
Lilienthal is the prototype "Airman."

Lilienthal's first glider was tailless, little more than a pair of
wings. He tested this glider by jumping off a board. Lilienthal's experiments
were soon to get more serious, however. He built an artificial conical hill
(visible in the background) at Lichterfelde, near Berlin, so he could
launch his gliders into the wind no matter which direction it was coming from.

No. 11 was the 'standard' Lilienthal model, a monoplane with a wing area
of 13 sq. m. At least eight replicas of this model were built, and either sold
or presented to clients. The National Space and Air Museum in the Smithsonian
has a No. 11 built by Lilienthal.

Lilienthal is the source of two famous quotes about inventing airplanes.
The first illustrates the discipline that must accompany creativity in
invention: "To invent an airplane is nothing. To build one is something. But
to fly is everything." The second was all too prophetic: "Sacrifices must be
made." He died August 10, 1896 from injuries sustained two days earlier in a
crash of one of his hang gliders.